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How much do you know about sexually transmitted diseases (STDs)? It turns out that most teens don't know much about STDs until they get one. And a lot of them are getting STDs. Half of all sexually active teens will catch chlamydia, herpes, or another STD by the time they turn 25.

WebMD talked to Gail Bolan, MD, director of the CDC's Division of STD Prevention, to find out more about STDs. She also has some important advice to help teens protect themselves every time they have sex.

How do I get an STD?

The way that you can get an STD is by having unprotected sex, and that means having vaginal sex, anal sex, or oral sex and not using a condom consistently and correctly.

Is there any way to tell if my partner has an STD?

A lot of people think that they can check out their partner or look at their partner and tell whether or not their partner has an STD. Unfortunately, that is not correct. Most of these STDs are what we call completely asymptomatic [they have no symptoms]. The only way you can tell that you have an STD is by going to see your health care provider and making sure your provider tests you.

How can I know for sure that I don't have an STD?

We recommend that you see a health care provider to be tested. The CDC has a special web site, findstdtest.org, where teens can go to find a nearby STD testing center. You can also text your ZIP code to 498669 (GYTNOW), and it will give you a list of clinics in your area where you can access STD testing.

Will the clinic have to tell my parents if I get tested?

Confidentiality is one of teens' biggest concerns about accessing care. But teens need to know that most states have laws that allow teenagers to get reproductive health services, and that includes contraception and STD testing, without parental consent. So I do encourage teens to call their local STD program, wherever they live, and find out what their state laws are for minors' consent for reproductive health care, diagnosis, and treatment.

For which STDs should I get tested?

We recommend that all sexually active teenage girls get a chlamydia test every year. We also recommend gonorrhea testing for teenage girls. Because we recognize that there's also a lot of HIV infection, although it's not as common in teenagers, we recommend that sexually active teenagers get at least one HIV test. Then, depending on their risk, their provider can decide whether or not they should get tested more often after that first test.

Syphilis is not as common in teenagers, so testing is not routinely recommended. But we do recommend if a teen ends up positive for chlamydia infection that they get tested for the other common STDs, which means gonorrhea, syphilis, and HIV. We don't recommend routine human papillomavirus (HPV) testing.

And of course, if your partner tests positive for an STD, you need to get yourself tested, as well.

How are STD tests done?

We have blood tests for HIV, syphilis, herpes, and hepatitis B. To be tested for chlamydia or gonorrhea, all the male needs to do is pee into a cup. A teenage girl can also pee into a cup. But if she has any kind of pelvic pain or discharge, then she needs to have a pelvic exam.

How are STDs treated?

There are different antibiotics for the treatable STDs, because the treatable STDs are all bacteria. Chlamydia is the most common STD. We typically use azithromycin (Zithromax), which can be given in a single dose [by mouth]. You can also take a drug called doxycycline for chlamydia. You have to take that twice a day for seven days. To treat gonorrhea, we recommend an injection of a drug called ceftriaxone. Syphilis is treated with an injection of penicillin.

Unfortunately for our viral STDs we don't have any treatments that cure them. If you become infected with herpes, that is a lifelong chronic viral infection. We can give people medication to decrease the symptoms, the severity of the symptoms, or the duration of the symptoms. The medication also decreases the amount of the virus that you shed, so it can make you less infectious.

How can I prevent STDs?

Abstinence is the first strategy for the best protection. Condoms are very effective for preventing chlamydia, gonorrhea, HIV, and hepatitis B. Use condoms consistently and correctly at all sites of exposure: in the mouth, in the rectum, and in the vagina. Also get tested on a regular basis.

Being in a mutually monogamous long-term relationship is another way that you can avoid STDs. Mutual monogamy means that you agree to be sexually active with only one person who's agreed to be sexually active only with you.

If you or your partner has been diagnosed with an STD, you should both get tested and ask your doctor how long you need to refrain from having sex to allow you both to clear the infection. That way, you won’t pass it back and forth.

Vaccination is another way that you can prevent yourself from becoming infected. So far the only effective vaccines we have available are for hepatitis B and HPV. We're recommending that teenage girls be vaccinated against HPV, because certain strains are associated with cervical cancer. We do know HPV is very common in teenagers who are sexually active, especially if they've had more than a couple of partners.

Do all condoms work against STDs?

Viruses can get through some of the natural skin condoms, so they don't protect against all sexually transmitted infections. We recommend the latex or polyurethane, which tend to be more expensive but need to be used by people who have latex allergies.

It's important that teens recognize that the condom needs to be put on as soon as there’s an erection. Not waiting until there's been a little foreplay, because there's ejaculate that can be released that can cause both STDs and unplanned pregnancies.

Even though it's so important to use a condom consistently and correctly, many teens don't know how. Health care providers, teen clinics, and educational materials can provide information on how to use a condom properly.